Radiant tube assembly

ABSTRACT

The radiant tube assembly includes a refractory or metal outer tube having a closed end and a concentric metal inner tube spaced therefrom to define an elongated, annular chamber between the two tubes. The inner tube has a plurality of apertures substantially along the length thereof and a restricted opening at the end thereof which communicate with the annular chamber. The inner tube cooperates with a burner and the outer tube cooperates with a discharge means at the burner end of the assembly. Products of combustion only and not flame exit from the inner tube through the various apertures and opening and circulate through the annular chamber and then exit through the discharge means.

United States Patent Rudin Sept. 5, 1972 [54] RADIANT TUBE ASSEMBLY [72] Inventor: Walter Rudin, Pittsburgh, Pa.

[73] Assignee: Bloom Engineering Company, Inc.,

Pittsburgh, Pa.

[22] Filed: Dec. 9, 1970 [21] Appl. No.: 96,443

52 US. Cl. .Q ..126/91 A 51 Int. Cl. ..F24c 3/00 581 Field of Search....l26/9l R, 91 A, 360 R, 360 A [56] v References Cited UNITED STATES PATENTS 3,285,240 11/1966 Schmidt 126/91 A 2,478,732 8/1949 Wilson et al. ..126/91 A x FOREIGN PATENTS OR APPLICATIONS 208,905 5/1960 Austria ..126/91 A 716,579 10/1954 Great Britain ..126/91 A 907,504 10/ 1962 Great Britain ..126/91 A Primary Examiner-Charles J. Myhre Attorney-Webb, Burden, Robinson & Webb ABSTRACT The radiant tube assembly includes a refractory or metal outer tube having a closed end and a concentric metal inner tube spaced therefrom to define an elongated, annular chamber between the two tubes. The inner tube has a plurality of apertures substantially along the length thereof and a restricted opening at the end thereof which communicate with the annular chamber. The inner tube cooperates with a burner and the outer tube cooperates with a discharge means at the burner end of the assembly. Products of combustion only and not flame exit from the inner tube through the various apertures and opening and circulate through the annular chamber and then exit through the discharge means.

7 Claims,5 Drawing Figures RADIANT TUBE ASSEMBLY This invention relates to radiant tube heating and, more particularly, to radiant tube assemblies usedin conjunction with radiant tube burners.

The conventional multi-leg radiation tube employed today in industry is often limited in application because of the need for a more compact system. In addition, a radiation tube has been needed which can act as an immersion tube for a molten bath.

Several attempts have been made to satisfy the above needs by providing a single leg radiant tube having a concentric inner tube communicating with the burner. This type of concentric tube arrangement has been designed so that the air-fuel mixture exits a series of openings in the inner tube at which time the mixture is ignited to heat the radiant outer tube. However, this type of arrangement is prone to causing hot spots on the outer tube and presents problems of safety since ignition must take place external of the several openings along the inner tube.

Attempts have also been made to fire into the inner tube and have the products of combustion exit through an unrestricted aperture at the end thereof. This also tends to cause nonuniform heating of the outer tube and requires ignition to take place at the discharge end of the inner tube, again presenting safety drawbacks.

My invention overcomes the problems of hot spots and provides an arrangement whereby the products of combustion sweep the outer tube to provide a uniform heating thereof. I have also eliminated the safety drawbacks of the known radiant tubes by having combustion take place at the burner end of the inner tube by igniting the fuel mixture. Because of the control of ignition of the burner entry end of the tube rather than at the discharge end, extremely large amounts of excess air can be employed while still maintaining a stable flame. In addition, through the aid of the restricted end opening of the inner tube, the back pressures created thereby aid in flame stabilization, control of fuel and uniformity of temperature along the outer tube.

My radiant tube assembly consists of an outer tube which can be either metal or refractory and a concentric inner tube made of metal. The burner which cooperates with the assembly directs a flame into the inner tube which has a series of apertures along its length and a restricted opening at the end thereof. The burner operation retains the flame within the inner tube and only the products of combustion exit from the apertures and the opening to uniformly heat the outer tube. A discharge means is positioned at the burner end of the assembly to exhaust the products of combustion.

' In the accompanying drawings, I have shown my presently preferred embodiments of my invention in which:

FIG. 1 is a section through my radiant tube assembly;

FIG. 2 is a section taken along section line II-II of FIG. 1;

FIG. 3 is an enlarged view of the discharge end of my assembly;

FIG. 4 is a section taken along section lines IV-IV of FIG. 3; and

FIG. 5 is an alternate arrangement of the discharge end of my assembly.

My radiant tube assembly can be used in any of the many environments which presently employ radiant tube heating. However, because of the extremely uniform temperature along the length of the radiant tube, my invention is particularly amenable to a molten bath where the tube is immersed therein to maintain the molten state.

My radiant tube assembly 10 includes an outer tube 12 and an inner tube 13 which is concentric therewith, see FIG. 1. Depending on the application of the radiant tube assembly, the outer tube can be either metal or a refractory. For example, where the tube will be used as an immersion tube in a bath of molten aluminum, an insert refractory such as silicon carbide can by employed. On the other hand, where the radiant tube will be used in a furnace chamber, the standard radiant tube metals will be employed. The inner tube 13 will be a metal such as stainless steel which will provide long wear and possess the desired heat transfer characteristics.

The inner tube 13 is spaced from the outer tube 12 to form an elongated, annular chamber 14 therebetween. When my radiant tube assembly is used in a horizontal position, lugs or spiders 21 such as shown in FIG. 1 are employed about the inner tube to maintain the desired concentricity of the inner tube 13 with respect to the outer tube 12. Where the radiant tube is used in the vertical position, such as for immersion into a molten bath, the spiders 21 need not be employed.

Inner tube 13 has a plurality of apertures 18 extending substantially the entire length of the inner tube. These openings can be aligned or staggered, although the preferred embodiment, FIGS. 1 and 2, show five sets of apertures along the length of the inner tube with each set having four equally spaced apertures in a plane normal to the inner tube 13. The end of the inner tube terminates in an opening 19 which is restricted in size so that its inside diameter is smaller than the inside diameter of the inner tube 13.

The inner tube 13 cooperates with the combustion chamber of a burner 11 which is mounted to mounting plate 15 by known means (not shown). Mounting plate 15 has a central opening through which inner tube 13 is snugly inserted. In addition to the snug fit, inner tube 13 is welded to the mounting plate 15 by welds 17. The burner 11 can be any of the several types employed with radiant tubes. I have shown one such burner having air inlet 25 feeding into an air chamber 26 and then through eight air openings 29 to mix with the gas directed into the burner through gas inlet 27. A flame retention nozzle 28 is employed to create combustion of the air and gas at the burner end of the inner tube 13. An igniter 30 cooperates with the burner adjacent the flame retention nozzle to ignite the air and gas mixture.

Outer tube 12 is offset from mounting plate 15 through four spaced supports 16. Supports 16 are connected to the mounting plate by a standard connection (not shown) but since the embodiment shown in FIG. 1 is specifically directed to an immersion tube and is positioned vertically in a molten bath, there is no need for a perma-nent connection between the outer tube 12 and the supports 16. The spaces 22 between the supports 16 form the discharge means for the products of combustion. The discharge means formed by spaces 22 exits the products of combustion directly into the at mosphere surrounding the radiant tube assembly, see FIGS. 3 and 4.

Where it is desired to exhaust the products of com bustion out of the vicinity of the radiant tube assembly,

a tee-type connection can be employed, such as the one shown in FIG. 5. There outer tube 12' cooperates with discharge pipe 35 at the burner end of the assembly. This tee-shaped connection can then be employed to exit the hot gases away from the radiant tube, for example, through a stack and out of a building.

My radiant tube assembly works as follows. The air and fuel is ignited by igniter 30. The flame is retained near the burner by the flame retention nozzle 28 as well as extending outwardly from the burner within the inner tube 13. The flame does not leave the inner tube 13 and the products of combustion, as shown by arrows 20, exit the inner tube 13 at the apertures 18 and at the restricted end opening 19. Because of the back pressureformed from the restricted end opening 19, the flame is maintained in a stable manner so that the products of combustion uniformly exit the various apertures 18 along the inner tube 13. The products of combustion uniformly wipe the end wall and the length of the outer tube 12 and exit through the spaces 22 into the atmosphere.

The back pressure resulting from the restricted end opening and the various apertures along the length of the inner tube permit excess air in excess of 600 percent to be employed and still retain a stable continuous flame. Many concentric types of radiant tubes require operating conditions that are reducing or close to stoichiometric in order to avoid flameouts and other safety problems. However, my radiant tube assembly can be continually operated as oxidizing and this, therefore, increases the life of the inner tube since the atmosphere is not constantly changing.

Actual dimensioning of the inner tube, the spacing of the apertures 18 and the restriction on the end opening 19 are a function of the length of the outer tube 12 and one skilled in the art will be able to make this determination based on the requirements of the radiant tube assembly. For best performance, the aperture-or series of apertures in the inner tube closest to the burner end should start at a point just beneath the bath level or just inside a furnace chamber, such as the case maybe. This then assures the uniformity along the entire length of the outer tube 12.

Thermocouples have been placed along the entire length of the outer tube and I have found that the temperature profile is substantially uniform throughout the length of the outer tube and that the restricted end orifice has eliminated any hot spots at the end of the outer tube. It should be noted that while the outer tube is shown at its terminal end in the form of a hemispherically closed tube, the terminal portion may be flat or may assume other shapes I claim:

1. A burner and radiant tube assembly combination comprising a burner, an outer tube having a closed end and a concentric inner tube spaced therefrom to define an elongated annular chamber therebetween, said outer tube adapted to cooperate with a mounting means at its open end and said inner tube adapted to extend beyond said mounting means to communicate with the burner, the annular chamber communicating with a discharge means at substantially the open end of the outer tube, said inner tube having a plurality of spaced apertures substantially along the length thereof and a restricted opening at the end thereof, said burner ififi lit t fiurfif'i ol'lfifililfr illfifi'il rilin the flame substantially within said inner tube, said apertures and opening communicating with the annular chamber so that products of combustion exit from the inner tube, circulate through the annular chamber and exit through the discharge means.

2. the radiant tube assembly of claim 1 wherein said outer tube is spaced from said mounting means by a plurality of spaced supports so that the products of combustion exit through the spaces between the separator supports, said spacers defining the discharge means.

3. The radiant tube assembly of claim 1 wherein said discharge means is a discharge pipe communicating with the annular chamber through an opening in the outer tube at substantially the open end thereof.

4. The radiant tube assembly of claim 1 wherein a spider cooperates with the inner and outer tubes to maintain the spaced relationship therebetween.

5. The radiant tube assembly of claim 1 wherein said apertures along the length of the inner tube are positioned in groups, each group having a series of openings equally spaced and in a plane normal to the inner tube.

6. The radiant tube assembly of claim 5 wherein there are four apertures in each group.

7. An immersion tube apparatus for insertion into a molten bath comprising a burner and a radiant tube assembly, said radiant tube assembly comprising an outer tube having a closed end and a concentric inner tube spaced therefrom to define an elongated annular chamber therebetween, said outer tube adapted to cooperate with a mounting means at its open end and said inner tube adapted to extend beyond said mounting means to communicate with the burner, the annular chamber communicating with a discharge means at substantially the open end of the outer tube, said burner including flame retention means to maintain combustion at the burner end of theinner tube and retain the flame substantially within said inner tube, said inner tube having a plurality of spaced apertures substantially along the length thereof and a restricted opening at the end thereof, said apertures and opening communicating with the annular chamber so that products of combustion exit from the inner tube, circulate through the annular chamber and exit through the discharge means, the apertures closest the burner being positioned to be just below the level of the molten bath. 

1. A burner and radiant tube assembly combination comprising a burner, an outer tube having a closed end and a concentric inner tube spaced therefrom to define an elongated annular chamber therebetween, said outer tube adapted to cooperate with a mounting means at its open end and said inner tube adapted to extend beyond said mounting means to communicate with the burner, the annular chamber communicating with a discharge means at substantially the open end of the outer tube, said inner tube having a plurality of spaced apertures substantially along the length thereof and a restricted opening at the end thereof, said burner including flame retention means to maintain combustion at the burner end of the inner tube and retain the flame substantially within said inner tube, said apertures and opening communicating with the annular chamber so that products of combustion exit from the inner tube, circulate through the annular chamber and exit through the discharge means.
 2. the radiant tube assembly of claim 1 wherein said outer tube is spaced from said mounting means by a plurality of spaced supports so that the products of combustion exit through the spaces between the separator supports, said spacers defining the discharge means.
 3. The radiant tube assembly of claim 1 wherein said discharge means is a discharge pipe communicating with the annular chamber through an opening in the outer tube at substantially the open end thereof.
 4. The radiant tube assembly of claim 1 wherein a spider cooperates with the inner and outer tubes to maintain the spaced relationship therebetween.
 5. The radiant tube assembly of claim 1 wherein said apertures along the length of the inner tube are positioned in groups, each group having a series of openings equally spaced and in a plane normal to the inner tube.
 6. The radiant tube assembly of claim 5 wherein there are four apertures in each group.
 7. An immersion tube apparatus for insertion into a molten bath comprising a burner and a radiant tube assembly, said radiant tube assembly comprising an outer tube having a closed end and a concentric inner tube spaced therefrom to define an elongated annular chamber therebetween, said outer tube adapted to cooperate with a mounting means at its open end and said inner tube adapted to extend beyond said mounting means to communicate with the burner, the annular chamber communicating with a discharge means at substantially the open end of the outer tube, said burner including flame retention means to maintain combustion at the burner end of the inner tube and retain the flame substantially within said inner tube, said inner tube having a plurality of spaced apertures substantially along the length thereof and a restricted opening at the end thereof, said apertures and opening communicating with the annular chamber so that products of combustion exit from the inner tube, circulate through the annular chamber and exit through the discharge means, the apertures closest the burner being positioned to be just below the level of the molten bath. 